What are the things that work in each of the seven layers of OSI?

The main function of the application layer in OSI Layer 7 is to provide interfaces for applications used for communication and the underlying network for message transmission.

The application layer is the seventh layer of the seven-layer OSI model. The application layer directly interfaces with the application and provides common web application services. The application layer also makes requests to the presentation layer.

The application layer is the highest layer of the open system and provides services directly to the application process. Its function is to realize the communication between multiple system application processes at the same time, complete a series of services required for business processing, and its service elements are divided into two categories: public application service element case and specific application service element SASE.

case provides the most basic service, which becomes the user of any user and any service element in the application layer, and mainly provides the basic control mechanism for application process communication and distributed system implementation;

Specific services such as document transfer, access management, job transfer, banking transactions, order entry, etc. These will involve virtual terminals, job transfer and operation, volume transfer and access management, remote database access, graphics core systems, open systems interconnection management, and more.

Layers 1 through 3 are responsible for creating links to network communication connections.

Layers 4 to 7 are responsible for end-to-end data communication.

1. Physical layer: specifies the characteristics of communication equipment and communication links.

2. Data link layer: On the basis of the bit stream provided by the physical layer, the data link between adjacent nodes is established, and the unreliable physical medium provides reliable transmission PPP protocol.

3. Network layer: select appropriate inter-network routing to complete multiple data links between two computers, through routing protocol and address resolution protocol (ARP). IP, RIP (Routing Information Protocol), OSPF (Shortest Path First Protocol).

4. Transport layer: provide end-to-end logical communication between applications.

5. Session layer: authentication access and session management.

6. Presentation layer: transformation of information format and syntax.

7. Application layer: provide available network interfaces for operating systems or applications.

The seven levels of the OSI (Open Systems Interconnection) reference model are the physical layer, the data link layer, the network layer, the transport layer, the session layer, the presentation layer, and the application layer.

OSI divides computer network architecture into the following seven layers:

Physical layer: Converts data into electronic signals that can be transmitted through a physical medium equivalent to a porter in a post office.

Data Link Layer: Determines how network media is accessed. At this layer, the data is framed and flow control is handled. This layer specifies the topology and provides hardware addressing, equivalent to a packer in a post office. Which seeps.

Network layer: Right-of-use data is routed through a large network equivalent to a sequencing worker in a post office.

Transport Layer: Provides a reliable end-to-end connection that is equivalent to a messenger in the company's post office.

Session layer: Allows users to make connections with easy-to-remember names Equivalent to the secretary in the company who receives and sends letters, writes envelopes, and opens envelopes.

Presentation layer: Negotiate the format of the data exchange, which is equivalent to the briefing boss in the company, and the assistant who writes letters for the boss.

Application layer: The interface between the user's application and the network.

OSI Reference Model.

It is divided into 7 layers, namely the physical layer and the data link layer.

Network Layer, Transport Layer, Session Layer, Presentation Layer, and BAI Application Layer.

The main functions of each layer and their corresponding data units are as follows:

1. Physical layer: To transmit information, it is necessary to use some physical cables, such as double new wires and coaxial cables.

However, the specific physical ** is not within the 7 layers of the OSI, and some people regard the physical ** as the 0th layer, and the task of the physical layer is to provide a physical connection to its upper layer, as well as their mechanical, electrical, functional and process characteristics.

2. Data link layer: The data link layer is responsible for the error-free transmission of data in frames on the line between two adjacent nodes. Each frame includes a certain amount of data and some necessary control information.

3. Network layer: There may be many data links between two computers communicating in a computer network, and there may also be many communication subnets.

4. Transport layer: The task of this layer is to make the best use of network resources according to the characteristics of the communication subnet, and to provide the function of establishing, maintaining and canceling the transmission connection between the session layer of the two end systems in a reliable and economical way, and is responsible for reliably transmitting data. At this level, the unit of transmission of information is the message.

5. Session layer: The session layer does not participate in specific transmission, but provides a mechanism for establishing and maintaining communication between applications, including access verification and session management. For example, the server authenticates the user login at the session level.

6. Presentation layer: This layer mainly solves the problem of grammatical representation of supporting information. It converts the data to be exchanged from an abstract syntax suitable for a user to a transfer syntax suitable for internal use in an OSI system.

7. Application layer: determine the nature of communication between processes to meet user needs and provide interface services between the network and user application software.

Layer 1: Physical layer.

To solve the problem of how to communicate between two pieces of hardware, common physical media include optical fiber, cable, repeater, etc. It mainly defines the standards of physical devices, such as the interface type of network cable, the interface type of optical fiber, and the transmission rate of various transmission media.

Layer 2: Data link layer.

The data link layer receives packets, packets, from the network layer.

Contains the IP addresses of the sender and receiver. The data link layer performs two basic functions. It allows the upper layer to access the media using various techniques such as framing, controlling how data from the medium is placed and received.

Layer 3: Network layer.

The transport layer passes data segments to the network layer. The network layer is used to transfer received segments of data from one computer to another computer located in a different network. The unit of data at the network layer is called a packet, and the functions of the network layer are logical addressing, routing, and path determination.

Layer 4: Transport layer.

The main task of the lower three layers of OSI is data communication, the task of the upper three layers is data processing, and the transmission layer is the fourth layer, so this layer is the interface and bridge between the communication subnet and the resource subnet, and plays the role of connecting the upper and lower layers.

Layer 5: Session layer.

It is the interface between the user application and the network, and its main task is to organize and coordinate the communication between the two session processes and to manage the data exchange.

Sixth layer: represents the layer.

The presentation layer receives data from the application layer, which is in the form of characters and numbers, and converts this data into a machine-understandable binary format, i.e., encapsulating and formatting data, such as converting ASCII code into other encodings, a function called "translation".

Layer 7: Application layer.

It is the highest layer of the OSI reference model, which enables the interface between computer users and various applications and networks, which are used by network applications, such as HTTPS protocol, HTTP protocol, and the application layer provides services to the network through the protocol and performs user activities.